This project is to elucidate the structure and functions of phosphofructokinase from various tissues. In the current year we will attempt to determine the physiological significance of phosphorylation and dephosphorylation of phosphofructokinase in vivo using rat diaphrams. The effect of glucose, epinephrine, insulin, etc. on the phosphorylation of this enzyme will be studied. We have separated rabbit muscle phosphofructokinase with low and high P forms of the enzyme. In order to search for a specific protein kinase and phosphatase, the low and high P forms of the enzyme will be used as the substrates, respectively. We also plan to characterized these two forms of the enzyme, in order to understand the effect of phosphorylation on its structure and regulating properties. We will also study the binding of phosphofructokinase to erythrocyte membrane including its binding site and further characterization of bound and free enzymes.